This invention relates to printing apparatus, and especially to roller type printing devices for applying various indicia to the surface of moving articles such as packages being successively conveyed. More particularly, the invention relates to an improved printing device for marking a surface by rolling an ink-carrying cylindrical printing segment against the surface to be marked.
In the manufacture and packaging of various goods, certain markings such as date codes, names, coded identifiers and the like are printed on the packages or products as they are being conveyed at a high rate of speed. Such packaging may be of metal, plastic or cardboard, for example, and in many instances the marking must be printed with considerable accuracy at a precise location on the rapidly moving surfaces. One type of marking for packages and products that has come into widespread use is optically readable characters such as scannable and verifiable bar codes. Bar codes comprise a series of parallel lines or bars of varying width and spacing, containing coded information that can be read by an optical device. These codes must be printed very accurately and without variation in the predetermined incremental dimensions. The printing machine must be capable of accurate marking regardless of variations in the shape, etc. of the surface to be marked.
Various printing devices and associated apparatus have been employed to make clear ink imprints at high speeds, certain of these being the subject of U.S. Pat. Nos. 3,071,071; 3,093,040; 3,122,993; 3,230,880; 3,327,624; 3,736,870; 3,968,747; 4,129,074; and 4,729,313.
The level of accuracy required in printing bar codes of sufficient sharpness and clarity to be read by an optical reader makes it extremely important that the application of ink to the typeface or marking pad of the printing roll be uniform and consistant. An insufficient application of ink to the type could result in an imprint that could not be accurately read by an optical reader and, conversely, and excess of ink could result in distortion that could likewise generate an inaccurate optical reading.
The apparatus of the present invention, however, resolves the difficulties indicated above and affords other features and advantages heretofore obtainable.